AVS 3011 – Eye Dissection – Special Senses

Key Concepts of Eye Dissection and Special Senses

• Five Major External Special Senses

  • Vision
  • Audition (hearing)
  • Tactile (touch)
  • Gustation (taste)
  • Olfaction (smell)

• Sensations

  • Result from stimuli leading to afferent impulses reaching the cerebral cortex.
  • Include somatic senses (pain, cold, heat, touch, pressure) and special senses.

• Sensory Receptors

  • End organs of afferent nerves; responsible for converting stimuli into action potentials.
  • Main Groups:
  • Exteroceptors: Detect external stimuli (skin sensations, hearing, vision)
  • Interoceptors: Detect internal stimuli (taste, smell, responses to pH, distention)
  • Proprioceptors: Signal deep body conditions; located in skeletal muscles, tendons, ligaments, and joint capsules.

Structure and Function of the Eye

• Receptor Organ for Vision:

  • Specific structures adapted for transparency allowing light rays to reach receptor cells.

• Eye Structure:

  • Eyeball (globe)
  • Optic Nerve
  • Accessory Structures: Eyelids, conjunctivae, lacrimal apparatus, muscles.

Exterior Structures of the Eye

• Fat

  • Purpose: Provides cushioning; loss of fat may cause sunken eyes in illness.

• Muscles

  • Innervated by cranial nerves for eye movement.
  • Holds eyeball in its orbit against fat pad.

• Optic Nerve

  • Bundle of nerve fibers transmitting visual information from retina to brain.

• Conjunctiva

  • Membranes lining eyelids; forms a conjunctival sac for tears.
  • Normal color: pink; pale indicates anemia; blue for lack of oxygen.
  • Inflammation = conjunctivitis.

• Tunics of the Eye

  1. Fibrous Tunic (outermost): Cornea and sclera.
  2. Vascular Tunic (Uvea): Choroid, ciliary body, iris.
  3. Nervous Tunic (innermost): Retina.
  • Retina contains photoreceptor cells converting light into electrical signals.

Key Eye Components

• Sclera: Tough, white layer; site for muscle attachment.
• Cornea: Transparent front portion covering iris and pupil; contributes to vision clarity.
• Aqueous Humor: Fluid filling anterior chamber of the eye; increase leads to glaucoma.
• Iris: Colored diaphragm; controls pupil size.
  • Muscles adjust pupil size in response to light.

Internal Structures of the Eye

• Lens

  • Transparent, biconvex structure that focuses light onto the retina.
  • Suspensory ligaments attach lens to ciliary body.
  • Accommodates according to object distance.
  • Conditions affecting lens: Lenticular sclerosis (grey tint in aging) and Cataract (clouding).

• Vitreous Body

  • Large cavity behind lens; helps maintain eye shape.

• Retina

  • Contains rods (night vision) and cones (color vision).
  • Fovea Centralis: Area of highest visual acuity.

• Choroid Layer

  • Pigmented, vascular layer preventing light reflection.

• Accessory Structures

  • Lacrimal glands produce tears; keep eye moist and clean.
  • Meibomian glands help form a tear barrier.

Accommodation and Visual Response

• Accommodation: Adjustment of lens shape to focus on objects at varying distances.

  • Relaxed lens: Flat for distant objects.
  • Contracted lens: More convex for near objects.

• Pupil Response

  • Changes in size based on light exposure; different responses in light vs. dim conditions.

Experimentation

• Accommodation Experiment: Visual focus shifting from near to far objects; observe lens status and response in ciliary muscles.
• Vision Response Test: Observe pupil dilation in different lighting conditions; explain physiological responses.

Overall Anatomical Context

• Optical Components:
  • Light passes through cornea, lens, and vitreous body before reaching retina.
  • Inverted image formed on the retina transmitted via optic nerve to the brain.

Vision Conditions

• Emmetropia: Normal vision.
• Hyperopia (Farsightedness): Difficulties focusing on near objects.
• Myopia (Nearsightedness): Difficulties focusing on distant objects.
• Field of Vision: Spatial perception affected by eye placement; overlapping fields enhance depth perception for predatory animals.

Dissection Protocol (Eye Dissection)

1. Begin with cow eye; observe exterior structures.
2. Remove cornea, lens, vitreous body; identify internal structures (aqueous humor, retina).
3. Repeat with pig and sheep eye.
4. Conduct experiments on accommodation and reflex responses.